1. Field of the Invention
The present invention relates to continuously variable ratio transmission systems.
2. Background Art
It is known to provide a continuously variable ratio transmission system having system input and output shafts and a continuously variable ratio transmission unit (known as a variator) connected to the system input shaft and having a variator output shaft. A mixing epicyclic gear train receives drive from the system input and from the variator input. By appropriate use of clutches or other braking elements, the system can operate in a high-gearing regime or a low-gearing regime. Examples of such transmissions, which disclose arrangements having coaxial system input and output shafts, can be found in JP-A-6-174033 and JP-A-62-255655.
Inevitably, small power losses arise from the intermeshing of gears. In order to maximise efficiency, it is therefore desirable to reduce the number of gear meshes, particularly in the mixing epicyclic gear train where the power losses can be effectively be magnified during operation in a “power recirculation” mode.
Our co-pending United Kingdom patent application 0212186.1 addresses this problem by providing a mixing epicyclic gear train having an input sun gear drivably connected to the variator output shaft, a planet carrier drivably connected to the system input shaft and a first planet gear mounted on the planet carrier and drivingly engaged with the input sun gear. The first planet gear drives a first intermediate output shaft arranged coaxially with the system input shaft and is selectively connectable to the system output shaft via a first clutch. In addition, the first planet gear provides the input for a second epicyclic gear train having an output which is selectively connectable to the system output shaft via a braking element.